Measurements of physical quantities are the corner stone upon which we humans have built the scientific perception of the world. Measurements are the distinctive means to tell the scientific truth apart from any other approach to knowledge. The fundamental concepts of measurement and uncertainty in measurement have been analysed with reference to authoritative documents produced by the International Bureau of Weights and Measures (BIPM). The need for the introduction of the concept of uncertainty and its theoretical implications are analysed. The practical consequences in the development of industrial products have been illustrated for a specific measurement in proton exchange-membrane fuel cell assembly. A short critical analysis of the relationship between the evaluation of uncertainty in measurement and intelligent systems led then to a few open questions.